Originally Posted by The Joker
If Bruce thought it was the wrong thing to do then he wouldn't have done it. He obviously felt he wasn't breaking his one rule. He didn't kill Ra's, he just didn't save him. His philosophy is he won't become an executioner. Ra's smashed the brakes on the train and created his own death trap.
Bruce should feel more guilt about blowing up the ninja lair than leaving Ra's on the train.
I think Bruce's philosophy is a little more than 'no kill people.' Batman is more than avoid killing someone.